Human sedative self-administration: effects of interingestion interval and dose.

In a residential hospital ward setting, either sodium pentobarbital, diazepam or ethanol was made availabe for oral ingestion to volunteer human subjects with documented histories of drug abuse. During specified portions of the day, tokens could be earned by riding an exercise bicycle and exchanged for doses of a drug. Increases in the required minimum interingestion interval from 0 to 30 minutes produced decreases in the number of ingestions of sodium pentobarbital and diazepam. In another experiment, increases in the dose per ingestion (30-90 mg of sodium pentobarbital, 2-10 mg of diazepam, or 1.86-11.14 g of ethanol) produced increases in the number of ingestions. In both experiments, the effects of the manipulated variable were similar for all of the drugs studied. The study demonstrates the feasibility of human self-administration research with the sedative drugs, sodium pentobarbital and diazepam, for which substantive experimental data have not previously been reported. In addition, the results indicate that both dose and minimum interingestion interval bear a systematic controlling relationship to the occurrence of drug self-administration behavior.